Photocurable compositions and method of forming topographical features on a membrane surface using photocurable compositions

ABSTRACT

Photocurable compositions and methods of preparation and use of such compositions. More particularly, photocurable compositions useful for forming topographical features on surfaces such as membrane surfaces. Methods of forming topographical features on a membrane surface using photocurable compositions.

BACKGROUND Field

The present invention relates to photocurable compositions and methodsof preparation and use of such compositions. More particularly, thepresent invention relates to photocurable compositions useful forforming topographical features, e.g., spacer features, on surfaces suchas membrane surfaces, and particularly on membranes used in osmosis andreverse-osmosis applications, such as membrane filters.

Brief Description Related Technology

Curable compositions have been used widely for sealing, adhesive,coating and potting applications, to name a few. The choice of the typebackbones and curable groups is generally selected with reference to thespecific end use application and the environment in which it is intendedto be used. Polymers having various degrees of unsaturated groups, aswell as other functionally crosslinking groups have been used.

Formation of spacer features on filtration devices and osmosis membranesused in such devices is known. The use of curable composition patternsprinted onto membrane surfaces serve as replacements for moreconventional mesh layers which allow liquid, such as water, to flow andalso to keep the filtration membranes apart by providing a spacingfunction. The formation of curable composition patterns on a membranehas been discussed as having distinct advantages over mesh layers,particularly because the patterns provide less obstruction of flow andless build-up of filter debris (commonly referred to as fouling).Moreover, spacers placed directly on the surface of the membrane mayhave a height reduced by 50% when compared to a convention mesh spacer.A smaller spacer height in a traditional mesh would not be possible asit would dramatically increase feed pressure as well as pressure dropacross the element. The smaller height of the printed spacers does notappear to reduce feed pressure significantly. The benefit of the smallerprinted spacer height is that it allows for more membrane to be rolledinto the element to produce the same specified diameter as thetraditional mesh at a greater spacer height. For example, in certaininstances, the printed spacers allow for 7 additional leaves to beutilized, for a total of 35 leaves rather than the traditional 28 leavesin the same 8 inch diameter element (i.e., 25% more). In other cases, 3more leaves may be added, for a total of 10 leaves rather than thetypical 7 leaves in a 4 inch diameter element (i.e., 40% more).

There are many difficulties in manufacturing, on a commercial scale,membranes having printed curable composition patterns, i.e. referred toherein as topographical features. The topographical feature must have asize and shape which provides sufficient spacing from the adjacentlayer, balanced with a minimum coverage of the surface area of themembrane to allow a maximum of fluid flow.

Moreover, many curable compositions cannot meet the requirements interms of chemical and temperature resistance to hold up to the cleaningcycles required for these applications. In addition, the curablecomposition is required to have high bond strengths to the membranewhile also not being too brittle to damage the membrane during rollingor too soft and flexible that will compress and lose the specifiedspacing required while under pressure in use.

While UV inks are capable of high aspect ratios and fast cures, they arelimited by how high they can print in a single pass. Generally, manypasses of curable composition deposition are required over the same areato build the heights required for these applications, which dramaticallyslows the printing speed and production of the final product. Standardlight cure acrylics (LCA's) or even gel LCA's are not able to meet therequirements necessary for achieving certain heights as they have lowaspect ratios. If jet printing is used (jetting) the impact velocity ofthe curable composition when it hits the membrane further reduces theaspect ratio. Jetting is able to double the print speeds, but at a greatloss to the aspect ratio.

Polyolefin (PO) hot melt curable compositions with gravure printingallows very fast production speeds of printed membranes, however, it hasthe slowest cure speed due to cooling, which can take 30 seconds ormore, and which requires larger accumulation space to not damage thepattern. The PO hot melt's aspect ratio is not adequate when used at thehigh viscosities necessary for gravure printing. Print height is limitedto maximum print height possible by a single print pass because multipleprints passes are not possible using this technique. Accordingly, theaspect ratio is limited by the limited print height. Moreover, the POhot melt process is prone to stringing and long start-up times withlarge membrane waste, which is very expensive in thismarket/application. Thus, in this market, the PO hot melt process is notan efficient process.

There is a need for a curable composition and a process of using suchcomposition which allows for high speed printing of topographicalfeatures on surfaces such as membranes, the curable composition beinglight curable and possessing rheological properties that allow for avolume of the curable composition to substantially maintain itsdimensions once applied, as well as during the removal of the templatein the application of the curable composition to the membrane surface.

SUMMARY

The present invention provides a means of satisfying the above-mentionedneed. The present invention provides photocurable compositions (i.e.,light curable compositions) and methods of preparation and use of suchcompositions. More particularly, the present invention relates tophotocurable compositions useful for forming topographical features onsurfaces such as membrane surfaces.

In one aspect of the invention there is provided a method of formingtopographical features on a membrane surface including the steps of:providing a membrane surface; providing a stencil or screen over themembrane surface, the stencil or screen having openings exposing themembrane surface for receiving a curable composition; depositing one ormore layers of curable composition into the stencil openings or screenopenings and onto the membrane surface to form the topographicalfeatures, the openings defining an approximate shape and size of thetopographical features; removing the stencil or screen to leave in placethe topographical features on the membrane; and curing the curablecomposition, wherein a single layer of the curable composition depositedin the depositing step produces topographical features have an aspectratio (height/width) from about 0.2 to about 2.

In another aspect of the present invention, there is provided a methodof forming topographical features on a membrane surface including thesteps of: providing a membrane surface; providing a stencil or screenover the membrane surface, the stencil or screen having openingsexposing the membrane surface for receiving a curable composition;depositing one or more layers of curable composition into the stencilopenings or screen openings and onto the membrane surface to form thetopographical features, the openings defining an approximate shape andsize of the topographical features; and removing the stencil or screento leave in place the topographical features on the membrane; whereinthe Thixotropic index (TI) (viscosity at 1 s⁻¹/viscosity at 10 s⁻¹) ofthe curable composition is about 2 to about 15, and the curablecomposition provides a topographical features aspect ratio(height/width) sufficient to substantially maintain the approximate sizeand shape of the feature during removal of the stencil from the membranesurface prior to cure.

In a further aspect of the present invention, there is provided a lightcurable composition including: a light curable component comprising abackbone selected from the group consisting of (meth)acrylates, epoxies,polyisobutenes (PIB), polyurethanes (PU), polyolefins (PO),ethylvinylacetates (EVA), polyamides (PA) and combinations thereof; anda light curing moiety; a cure system; and rheology modifying componentpresent in an amount of about 2% to about 50% by weight of the totalcurable composition; wherein the curable composition has a ThixotropicIndex (TI) (cp at 1 s⁻¹/cp at 10 s⁻¹) of between about 2 and about 15.

In yet another aspect of the present invention, there is provided areverse osmosis filter including: a water permeable membrane having apattern of curable composition spacers printed thereon, wherein thecurable composition spacers are formed from a light curable compositionwith viscosity of 10,000 to 500,000 centipoise (cP) at 10 s⁻¹, aThixotropic Index (TI) (viscosity at 1 s⁻¹/viscosity at 10 s⁻¹) ofbetween about 2 and about 15, wherein the spacers are formed by stencilprinting or screen printing one or more spacer layers having an aspectratio (height/width) between about 0.2 and about 2.

In still another aspect of the present invention, there is provided amethod of manufacturing a filtration membrane having printed curablecomposition spacers including the steps of: providing a membrane have afirst surface and an opposing second surface; and depositing a lightcurable composition onto the first and/or second membrane surface(s) toform spacer features having a defined shape and size; wherein the lightcurable composition has viscosity of 10,000 to 500,000 centipoise (cP)at 10 s⁻¹, a Thixotropic Index (TI) (viscosity at 1 s⁻¹/viscosity at 10s⁻¹) of between about 2 and about 15 and wherein the aspect ratio(height/width) of the curable composition is between about 0.2 and about2.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a typical pattern of topographical features fordesalination of water or filtration of brackish water.

FIGS. 2a and 2b show a stencil and membrane arrangement, with openingsfor deposition of a curable composition, on a membrane surface, in theform of topographical features (showing three dimension) having adesired size and shape, the topographical features being sufficient toperform a spacing function when layered with other membrane surfaces.The aspect ratio (which provides for a desired spacing capability) ofthe features is shown. FIG. 2a shows the stencil overlaid on themembrane surface and FIG. 2b shows the stencil and membrane separatedfrom one another after the stencil has been removed from the membraneleaving the topographical features.

DETAILED DESCRIPTION

The present invention is directed to photocurable compositions andmethods of preparation and use of such compositions. More particularly,the present invention relates to photocurable compositions useful forforming topographical features on surfaces such as membrane surfaces.

A method of forming topographical features on a membrane surfaceaccording to the present invention includes the steps of: providing amembrane surface; providing a stencil or screen over the membranesurface, the stencil or screen having openings exposing the membranesurface for receiving a curable composition; depositing one or morelayers of curable composition into the stencil openings or screenopenings and onto the membrane surface to form the topographicalfeatures, the openings defining an approximate shape and size of thetopographical features; removing the stencil or screen to leave in placethe topographical features on the membrane; and curing the curablecomposition, wherein a single layer of the curable composition depositedin the depositing step produces topographical features have an aspectratio (height/width) from about 0.2 to about 2.

Another method of forming topographical features on a membrane surfaceaccording to the present invention includes: the steps of: providing amembrane surface; providing a stencil or screen over the membranesurface, the stencil or screen having openings exposing the membranesurface for receiving a curable composition; depositing one or morelayers of curable composition into the stencil openings or screenopenings and onto the membrane surface to form the topographicalfeatures, the openings defining an approximate shape and size of thetopographical features; and removing the stencil or screen to leave inplace the topographical features on the membrane; wherein the viscosityof the curable composition is 10,000 to 500,000 centipoise (cP) at 10s⁻¹, Thixotropic index (TI) (viscosity at 1 s⁻¹/viscosity at 10 s⁻¹) isabout 2 to about 15, and the curable composition provides atopographical features aspect ratio (height/width) sufficient tosubstantially maintain the approximate size and shape of the featureduring removal of the stencil from the membrane surface prior to cure.

The methods of the present invention may be carried out using high speedproduction printing methods known in the art. Preferably, the methods ofthe invention employ direct printing via stencil/screen or gravureprinting methods.

As shown in FIG. 2a , the membrane (10) is overlaid with the stencil(20) on one of the membrane's surfaces (not shown). The openings (30) inthe stencil are filled with curable composition to form thetopographical features (40). As shown in FIG. 2b , when the stencil (20)is removed from the membrane (10) the topographical features (40) formedfrom the curable composition are left attached to the membrane surface(50).

The topographic features formed on the membrane surface by the methodsof the present invention have physical characteristics that make themsuitable for providing spacing between overlaid layers of the membrane.For example, the topographic features may provide adequate spacingbetween layers of a spiral reverse osmosis filtering membrane tooptimize the operation, cleaning, and lifespan of reverse osmosismembrane elements employing membranes with these topographical features.Moreover, the topographical features are typically smooth or flat, withno sharp edges that may damage the mating layer of membrane duringoperation.

The aspect ratio of the topographical features may be greater than 0.50or greater than about 0.70. A combination of aspect ratios may be usedin a pattern to provide a specified spacing configuration between layersof membrane or other surfaces in the osmosis devices of the invention.As used herein, the term “aspect ratio” means the ratio of the height ofthe topographical features to the width of the topographical features.

The height of the topographical features once formed on the membrane maybe from about 0.001 to about 0.05 inches, such as from about 0.01 toabout 0.04 inches. The height of a topographical feature is the distancefrom the base of the topographical feature (on the membrane surface orthe interface between the topographical feature and the membrane) to thepoint on the topographical feature that is farthest perpendicularly fromthe membrane surface.

The width of the topographical feature is defined as the minimaldimension of a topographical feature footprint on a membrane surface,wherein the footprint is area or region of coverage on the substratesurface.

The pattern of topographical features may have a size and shapesufficient to maintain adequate membrane spacing and to exposesufficient membrane surface to ensure efficient operation of themembrane. In particular, the total surface area of the membrane coveredby the topographical features (i.e., area of the footprint of theindividual topographical features multiplied by the number oftopographical features per unit area of the membrane surface) is notmore than about 20% of the surface of the membrane (i.e., at least about80% of the membrane surface remains exposed). The total surface area ofthe membrane covered by the topographical features is not more thanabout 15%, such as not more than about 10%, or not more than about 6%,or not more than about 5%, or not more than about 3%, or note more thanabout 2%, or not more than about 1%.

The pattern of topographical features may be formed on the membranesurface at speeds of about 0.5 m²/minute or greater. The pattern oftopographical features may be formed on the membrane surface at speedsof about 1 m²/minute or greater or at speeds of about 2 m²/minute orgreater.

The printing speed of the topographical features may also be optimizedbecause the desired height may be achieved while only depositing asingle layer of curable composition without adversely affecting theaspect ratio and the overall membrane efficiency (as opposed to havingto coat and cure 10-20 layers of UV Ink, for example.) Moreover, thissingle layer of deposition is also carried out over the entire 40 inchwidth of the membrane simultaneously. Thus, the time for printing asingle leaf is the linear rate of travel down the length of the leaf(also 40 inches). Accordingly, there is no need for travel in both the Xand Y direction with multiple passes. Essentially, there is no need todeposit multiple layers of curable composition to achieve the desiredheight prior to curing or pre-curing on the membrane. This offerssignificant speed advantage over other technologies. By way of example,UV inks deposit maximum of 0.001 inch of height per pass. The processescan in the wet printing method deposit 10 times that, i.e., up to 0.010inch per pass and the pre-cure method can deposit 40 times that, i.e.,up to of 0.040 inch per pass. The processes are also capable ofdepositing less than the maximum heights in a single pass for fullflexibility in topographical feature design.

The surface upon which the topographical features are deposited mayinclude any surface though a membrane surface is most suitable. As usedherein, a “membrane” means a selective barrier that allows passage ofsome substances but prevents passage of other substances. The membranemay be a filter membrane, i.e., a membrane for filtering substances outof a liquid carrier, such as water. Filter membranes include reverseosmosis membranes, forward osmosis membranes, microfiltration membranes,ultrafiltration membranes, and nanofiltration membranes. Thetopographical features may be printed on the active surface of themembrane, or on the non-active surface of the membrane, or both. Thefilter membranes may be used in the assembly of devices used in energyproduction, such as by reverse electrodialysis or pressure retardedosmosis (e.g., salinity gradient power generation or osmotic powergeneration).

The curable composition may be deposited into and/or through the stencilor screen openings and onto the membrane surface to form thetopographical features by depositing a single layer of the curablecomposition. The curable composition may be deposited into and/orthrough the stencil or screen openings and onto the membrane surface toform the topographical features by depositing multiple layers of thecurable composition. The topographical features may be deposited on onesurface (either the feed side or permeate side) or both surfaces of themembrane.

The stencil or screen may be constructed from any useful material thatallows for adequate sealing of the stencil to the surface to prevent thecurable composition from bleeding onto the portion of the surfacecovered by the stencil and also allow for removal of the stencil fromthe surface without damaging the surface or disturbing the depositedcurable composition. The stencil or screen may be constructed from ametal, such as steel, aluminum, stainless steel, polymer coated metal,ceramic coated metal, metal fabric, composite materials, polymericmaterials, such as polyester or fluoropolymers, or polymer fabric.

A stencil printing method uses a stencil made from a single sheet ofmaterial in which a pattern is cut. The stencil is mounted into a frameand may also be mounted to a frame with a mesh to provide tightness,flatness and spring. The mesh may be constructed of any suitablematerial, for example stainless- steel, nylon, plastic, carbon fiber, orthe like. The thickness of the stencil will be the height of the featurebeing printed, minus the effects of gravity and physics that reduce theheight by a certain factor during printing (typically about 20%). Thepattern and openings size (apertures) also determine how much productcan be released out of a maximum thickness stencil. A stencil with asuperior surface with low surface energy will provide higher releasefrom the stencil. The wet printing method is limited to a height about20% lower than the stencil thickness. However, in the pre-cure method,using the stencil as a mold, the product pre-cures to the height of thestencil. Thus, the features can be released from the apertures of thestencil because the curable composition is not fully cured and due tothe low surface energy coating of the stencil. After the curablecomposition is fully cured, the height of the features is the same asthe height of the stencil.

A screen printing method uses a stainless-steel mesh or a polyester orNylon screen, which has an emulsion applied thereon to cover portions ofthe screen or mesh and expose a pattern into which the curablecomposition is deposited. Print thickness is dependent on the meshthickness, mesh open area, and emulsion build-up thickness. Thickness isalso affected by printer variables such as squeegee pressure anddurometer, angle of attack, speed, and snap-off distance. The viscosityof printing materials may vary from low to high depending on theapplication needs.

The openings or apertures in the stencil or screen pattern of thepresent invention may take any shape or combination of shapes requiredto produce a desired shape for the topographical features. For example,the openings may be shaped as circles, ovals, arcs, squares, rectangles,diamonds, pentagons, hexagons, stars, chevrons, or any combinationthereof. Such opening shapes produce three dimensional topographicalfeatures having a cross-section corresponding to the shape(s) of theopenings and having the height and aspect ratio described herein. Forexample, a circular opening will produce a cylindrical topographicalfeature. An example topographical of a feature pattern for desalinationof water or filtration of brackish water is shown in FIG. 1. The depthof the stencil will determine the height of the topographical featureand is chosen for the desired height in accordance with the aspectratios desired. For example, the heights may be from about 0.005 toabout 0.04 inches and desirably about 0.010 to about 0.025 inches, morepreferably from about 0.012 to about 0.015 inches.

The topographical features may be substantially free of sharp edgesafter formation and removal of the stencil. For example, the edges ofthe openings of the stencil may be free of any sharp edges so that thedeposited curable composition does not have sharp edges. Moreover, whenthe stencil or screen is removed the curable composition does not pullup with the stencil or screen causing sharp edges on the topographicalfeature. Essentially, the curable composition slumps enough to maintaina rounded or flat surface, but the curable composition does not slumpenough to lose the aspect ratio. In addition, the stencil coating ischosen to have low enough surface energy to avoid pulling the curablecomposition when the stencil or screen is removed. Thus, thetopographical features are typically smooth or flat, with no sharp edgesthat may damage the mating layer of membrane during operation.

The curable composition is capable of producing the thixotropic indexvalues and aspect ratios as described herein, as well as being lightcurable and suitable for use in the high speed production printingmethods. The curable compositions should have properties that make themsuitable for the high speed production printing methods described hereinand known in the art. For example, the curable compositions shouldprovide for fast cure speeds, desirable rheological properties, superioradhesion, chemical/temperature resistance, and flexibility/durability tomeet the various membrane application requirements.

The curable composition should have an optimized rheology that iseffectively balanced to allow for shear thinning to flow through ascreen or into the stencil printer but maintain its three dimensionalprint dimensions, e.g. height, width and depth (and thus maintain itsoverall shape), after the screen or stencil is removed to provide theaspect ratios described herein. Essentially, the curable composition ofthe present invention must exhibit a sufficient thixotropy to maintainits physical structure, and not run or sag, prior to cure. Moreover,when sheer force is applied (e.g., during depositing into the stencil orscreen) the curable composition's viscosity is lower, which aids in thecurable composition moving through/filling the openings in the stencilor screen. As used herein, “thixotropy” means that the substance becomesless viscous when stress (for example mixing or shaking) is applied andis more viscous when free of such stress (e.g., under staticconditions).

Generally, the curable composition should be capable of being depositedinto the stencil openings and onto the membrane surface, and oncedeposited and allowed to become static, capable of maintaining its shapeduring removal of the stencil and during curing.

The curable composition should have a thixotropic index (TI) of from 2to about 12, preferably from about 5 to about 10, and more preferablyfrom about 6 to about 8. The TI should be greater than about 2, greaterthan about 4, greater than about 6, greater than about 7, greater thanabout 8, greater than about 9, greater than about 10, or greater thanabout 11. As used herein, the “thixotropic index” means the ratio of theviscosity (in centipoise) of the curable composition at a speed of 1sec-1 to the viscosity (in centipoise) of the curable composition at aspeed of 10 sec-1 (viscosity at 1 s⁻¹/viscosity at 10 s⁻¹).

The curable composition should have a viscosity (in centipoise) at aspeed of 10 s⁻¹ of about 10,000 to about 500,000. The viscosity may bedetermined using known methods, for example, cone and plate rheometer,parallel plate rheometer, or rotation viscometer, such as Brookfieldviscometer.

The curable composition should have a cure speed of about 5 seconds orless. The curable composition should have a cure speed of about 4seconds or less, about 3 seconds or less, about 2 seconds or less, about1 seconds or less.

The curable composition may be a photocurable or light curablecomposition, i.e., curable when exposed to radiation in theelectromagnetic spectrum, such as by using light such as visible orultraviolet light (UV). Thus, the curable composition may be cured usinga light source, such a bulb or LED that produces visible or UV light.The curable composition is at least partially cured by exposing the sideof the membrane without the topographical features to the light source,typically a visible light source.

The curable composition may be fully cured before or after the removalof the stencil or screen.

The curable composition may also be pre-cured, i.e., partially cured,prior to removal of the stencil. Here, this partial curing is producedby exposing the side of the membrane without the topographical featuresto a visible light source. After the removal of the stencil or screen,the curable composition may then be fully cured using a UV or visiblelight source.

In this pre-cure method, the viscosity of the curable composition isincreased prior to removal of the stencil or screen to aid inmaintaining the shape of the topographical features during removal ofthe stencil. In some instances, this pre-curing gels the curablecomposition or partially cures the curable composition to a semi-solidstate. As discussed above, the stencil or screen is made from a coatedmetal that provides a low surface energy to allow the release of thecurable composition from the stencil via the limited adhesion created tothe membrane during the pre-cure.

This pre-cure method allows for dramatically improved aspect ratios overwet printing as it can achieve any height desired in one step (i.e.,0.005-0.040 inches), instead of requiring deposition of multiple layersto reach the necessary height).

There is also provided a light curable composition including a lightcurable component comprising a backbone selected from (meth)acrylates,epoxies, polyisobutenes (PIB), polyurethanes (PU), polyolefins (PO),ethylvinylacetates (EVA), polyamides (PA) and combinations thereof; anda light curing moiety; a cure system; and rheology modifying componentpresent in an amount of about 2% to about 50% by weight of the totalcurable composition. The curable composition should have a viscosity ofabout 10,000 to about 500,000 centipoise (cP) at 10 s⁻¹, and aThixotropic Index (TI) (viscosity at 1 s⁻¹/viscosity at 10 s⁻¹) ofbetween about 2 and about 15.

Materials used to make polymer backbones for the light curablecompositions include, but are not limited to, (meth)acrylates such as(meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate,n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl(meth)acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate,n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl(meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate,2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate,dodecyl (meth)acrylate, phenyl (meth)acrylate, tolyl (meth)acrylate,benzyl (meth)acrylate, 2-methoxyethyl (meth) acrylate, 3-methoxybutyl(meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth)acrylate, stearyl (meth) acrylate, glycidyl (meth) acrylate,2-aminoethyl (meth) acrylate, γ-(methacryloyloxypropyl)trimethoxysilane,(meth)acrylic acid-ethylene oxide adduct, trifluoromethylmethyl(meth)acrylate, 2-trifluoromethylethyl (meth)acrylate,2-perfluoroethylethyl (meth) acrylate,2-perfluoroethyl-2-perfluorobutylethyl (meth) acrylate, 2-perfluoroethyl(meth) acrylate, perfluoromethyl (meth) acrylate,diperfluoromethylmethyl (meth) acrylate,2-perfluoromethyl-2-perfluoroethylmethyl (meth) acrylate,2-perfluorohexylethyl (meth) acrylate, 2-perfluorodecylethyl (meth)acrylate, 2-perfluorohexadecylethyl (meth)acrylate, etc.; styrenicmonomers such as styrene, vinyltoluene, α-methylstyrene, chlorostyrene,styrenesulfonic acid and its salt; fluorine-containing vinyl monomerssuch as perfluoroethylene, perfluoropropylene, vinylidene fluoride,etc.; silicon-containing vinyl monomers such as vinyltrimethoxysilane,vinyltriethoxysilane, etc.; maleic anhydride, maleic acid, monoalkylesters and dialkyl esters of maleic acid; fumaric acid and monoalkylesters and dialkyl esters of fumaric acid; maleimide monomers such asmaleimide, methylmaleimide, ethylmaleimide, propylmaleimide,butylmaleimide, hexylmaleimide, octylmaleimide, dodecylmaleimide,stearylmaleimide, phenylmaleimide, cyclohexylmaleimide, etc.;nitrile-containing vinyl monomers such as acrylonitrile,methacrylonitrile, etc.; amide-containing vinyl monomers such asacrylamide, methacrylamide, etc.; vinyl esters such as vinyl acetate,vinyl propionate, vinyl pivalate, vinyl benzoate, vinyl cinnamate, etc.;alkenes such as ethylene, propylene, etc.; conjugated dienes such asbutadiene, isoprene, etc.; vinyl chloride, vinylidene chloride, allylchloride and allyl alcohol. These monomers may be used each alone or aplurality of them may be copolymerized.

Suitable examples of epoxies useful for making or incorporating into thebackbones of the light curable compositions include, but are not limitedto, bisphenol A epoxies, bsiphenol F epoxies, novolac epoxies, aliphaticepoxies, glycidylamine epoxies, and cycloaliphatic epoxies.

Suitable examples of polyisobutenes (PIB) useful for making orincorporating into the backbones of the light curable compositionsinclude, but are not limited to, polyisobutylene diacrylate as describedin U.S. Patent Application Publication No. 2014/0243444A1.

Suitable examples of polyurethanes (PU) useful for making orincorporating into the backbones of the light curable compositionsinclude, but are not limited to, polyester urethane acrylate andpolyether urethane acrylate.

Suitable examples of polyolefins (PO) useful for making or incorporatinginto the backbones of the light curable compositions include, but arenot limited to, UC-102M and UC-203M by Kuraray, polyethylacrylate andpolybutylacrylate as described in U.S. Pat. Nos. 7,781,494 and6,720,395.

The light curing moiety is attached to the polymer backbone, desirablybut not necessarily, at the terminal ends of the polymer backbone, andmaybe be any chemical moiety or group which when exposed to actinicradiation, such a LED, visible or UV light, cures via a crosslinkingreaction. For example, vinyl groups, (meth)acrylate, and epoxy groups.

The light curable component includes a material selected from a urethane(meth)acrylate and a (meth)acylate.

The cure system includes at least one cure initiator, and optionally, asensitizing compound capable of absorbing radiation in the appropriaterange of about 300-1000 nm and/or an electron donor. The cure initiator(or, photoinitiator), may be a UV initiator, a visible initiator or acombination of UV and visible initiators.

A variety of UV initiators may be employed. UV initiators are generallyeffective in the range of about 200 to about 400 nm, and particularly inthe portion of the spectrum that borders on the visible portion ofgreater than about 200 nm to about 390 nm.

Initiators that respond to UV radiation to initiate and induce curing ofthe (meth)acryl functionalized curable component, which are useful inthe present invention include, but are not limited to, benzophenone andsubstituted benzophenones, acetophenone and substituted acetophenones,benzoin and its alkyl esters, xanthone and substituted xanthones,phosphine oxides, diethoxy-acetophenone, benzoin methyl ether, benzoinethyl ether, benzoin isopropyl ether, diethoxyxanthone,chloro-thio-xanthone, N-methyl diethanol-amine-benzophenone,2-hydroxy-2-methyl-l-phenyl-propan-1-one,2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone andmixtures thereof.

Examples of such UV initiators include initiators available commerciallyfrom IGM Resins under the “IRGACURE” and “DAROCUR” tradenames,specifically “IRGACURE” 184 (1-hydroxycyclohexyl phenyl ketone), 907(2-methyl-1-[4- (methylthio)phenyl]-2-morpholino propan-l-one), 369(2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanone), 500(the combination of 1-hydroxy cyclohexyl phenyl ketone andbenzophenone), 651 (2,2-dimethoxy-2-phenyl acetophenone), 1700 (thecombination of bis(2,6-dimethoxybenzoyl-2,4,4-trimethyl pentyl)phosphine oxide and 2-hydroxy-2-methyl-l-phenyl-propan-1-one), and 819[bis(2,4,6-trimethyl benzoyl)phenyl phosphine oxide], and “DAROCUR” 1173(2-hydroxy-2-methyl-1-phenyl-1-propane) and 4265 (the combination of2,4,6-trimethylbenzoyldiphenyl-phosphine oxide and2-hydroxy-2-methyl-1-phenyl-propan-1-one); and2,4,6-trimethylbenzoyldiphenylphosphine oxide (commercially available asLUCIRIN TPO from BASF Corp.). Of course, combinations of these materialsmay also be employed herein. Of course, it is understood that some ofthese photoinitiators categorized herein as UV photoinitiators have atailing absorption into the visible range, and thus straddle the linebetween UV and visible light cure initiators, but nonetheless areincluded herein as part of the invention.

Initiators suitable for use that respond to visible light to initiateand induce curing include, but are not limited to, camphorquinoneperoxyester initiators, 9-fluorene carboxylic acid peroxyesters, visiblelight [blue] photoinitiators, d1-camphorquinone, “IRGACURE” 784DC(photoinitiator based on substituted titanocenes), and combinationsthereof.

Other suitable photoinitiator systems include those disclosed in each ofthe following patents or publications, each of which is incorporated byreference herein in its entirety. U.S. Pat. No. 4,505,793 to Tamoto etal., which is incorporated by reference herein, disclosesphotopolymerization initiators that include a combination of a3-keto-substituted cumarin compound and an active halogeno compound. Anumber of exemplary compounds are disclosed. Such photopolymerizationinitiators cure by exposure to light having wavelengths ranging betweenabout 180 nm and 600 nm. U.S. Pat. No. 4,258,123 to Nagashima et al.,which is incorporated by reference herein, discloses photosensitiveresin compositions including initiator components that generate a freeradical upon irradiation with actinic light. Such components includevarious triazine compounds, as more fully described therein.

Cationic photoinitiators for epoxy cure include diaryliodonium salts,triarylsulfonium salts, and phenacylsulfonium salts. Commerciallyavailable cationic photoinitiator include Omnicat 432 (triarylsulfoniumhexafluorophosphate salts), Omnicat 440 (4,4′-dimethyl-diphenyl iodoniumhexafluorophosphate), and Omnicat 550(10-biphenyl-4-yl-2-isopropyl-9-oxo-9H-thioxanthen-10-iumhexafluorphosphate).

Additional useful components may be found in European Patent PublicationNo. EP 0 369 645 A1, which discloses a three-part photoinitiator systemwhich includes a trihalomethyl substituted-s-triazine, a sensitizingcompound capable of absorbing radiation in the range of about 300-1000nm and an electron donor. Exemplary sensitizing compounds are disclosed,including: ketones; coumarin dyes; xanthene dyes; 3H-xanthen-3-one dyes;acridine dyes; thiazole dyes; triazine dyes; oxazine dyes; azine dyes;aminoketone dyes; methane and polymethine dyes; porphyrins; aromaticpolycyclic hydrocarbons; p-substituted aminostyryl ketone compounds;aminotriaryl methanes; merocyanines; squarylium dyes; and pyridiniumdyes. Exemplary donors also are disclosed, including: amines; amides;ethers; ureas; ferrocene; sulfinic acids and their salts; salts offerrocyanide; ascorbic acid and its salts; dithiocarbamic acid and itssalts; salts of xanthates; salts of ethylene diamine tetraacetic acid;and salts of tetraphenylboronic acid. Such initiators are sensitive toboth UV and visible light.

Additional useful components may be found in European Patent PublicationNo. EP 0 563 925 A1, which discloses photopolymerization initiatorsincluding a sensitizing compound that is capable of absorbing radiationin the range of about 250-1000 nm and2-aryl-4,6-bis(trichloromethyl)-1,3,5-triazine. Exemplary sensitizingcompounds that are disclosed include: cyanine dye, merocyanine dye,coumarin dye, ketocoumarin dye, (thio)xanthene dye, acridine dye,thiazole dye, thiazine dye, oxazine dye, azine dye, aminoketone dye,squarylium dye, pyridinium dye, (thia)pyrylium dye, porphyrin dye,triaryl methane dye, (poly)methane dye, amino styryl compounds andaromatic polycyclic hydrocarbons. These photopolymerization initiatorsare sensitive to UV and visible light.

U.S. Pat. No. 5,395,862 to Neckers et al., which is incorporated byreference herein, discloses fluorone photoinitiators, which aresensitive to visible light. Such fluorone initiator systems also includea coinitiator, which is capable of accepting an electron from theexcited fluorone species. Exemplary coinitiators are disclosed,including: onium salts, nitrohalomethanes and diazosulfones. U.S. Pat.No. 5,451,343 to Neckers et al., which is incorporated herein byreference, discloses fluorone and pyronin-Y derivatives as initiatorsthat absorb light at wavelengths of greater than 350 nm. U.S. Pat. No.5,545,676 to Palazzotto et al., which is incorporated by referenceherein, discloses a three-part photoinitiator system, which cures underUV or visible light. The three-part system includes an arylidonium salt,a sensitizing compound and an electron donor. Exemplary iodonium saltsinclude diphenyliodonium salts. Exemplary sensitizers and electrondonors for use in the three-part system also are disclosed.Additionally, the sensitizer is capable of absorbing light in the rangeof about 300-1000 nm.

The initiators set forth above are for the purposes of illustration onlyand are in no way meant to limit the initiators that may be used in thepresent invention.

Initiators may be employed in amounts of about 0.1% to about 10% byweight of the total composition. More desirably, the initiator ispresent in amounts of 0.5% to about 5% by weight of the totalcomposition.

As used herein, “rheology modifying component” means a composition orcompound that changes the rheological properties, e.g., viscosity orflow, of the curable composition. Suitable rheology modifying componentsinclude organic and inorganic ones. Inorganics include silica, silicate,alumina, asbestos, barium sulphate, calcium carbonate, calcium fluoride,carbon black, clays, diatomaceous earth, feldspar, ferromagnetics, flyash, glass fibers, gypsum, jute fiber, kaolin, lingnocellulosics,magnesium hydroxide, mica, microcrystalline cellulose, powdered metals,quartz, startch, talc, titanium dioxide, wood flour, wood fibers, andcombinations thereof. Organic rheology modifiers include thermoplasticpoymers such as polyvinylacetate, polyolefine, nylon fibers. In anaspect of the present invention, the rheology modifying component ispresent in amounts of about 2% to about 80% by weight based on the totalweight of the curable composition. In another aspect of the presentinvention, the rheology modifying component is present in amounts ofabout 4% to about 50% by weight based on the total weight of the curablecomposition. In other aspects of the present invention, the rheologymodifying component is present in amounts of about 5%, or about 10%, orabout 15%, or about 20% or about 25%, or about 30%, or about 35%, orabout 45%, or about 55%, or about 60%, or about 65%, or about 75% weightbased on the total weight of the curable composition.

Optional additives, such as, but not limited to, stabilizers,inhibitors, oxygen scavenging agents, fillers, dyes, colors, pigments,adhesion promoters, plasticizers, toughening agents, reinforcing agents,fluorescing agents, wetting agents, antioxidants and combinationsthereof also may be included in the compositions of the presentinvention.

The curable composition, once cured, should lose less than about 5%weight when submerged in a aqueous solution at a pH range of about 0.5to about 13.5 at temperatures of from about 25° C. to about 90° C. forin a 6 week period.

The curable composition should be capable of forming and maintainingtopographical surface features having an aspect ratio (height/width) ofgreater than about 0.5 prior to cure.

There is also provided a reverse osmosis filter including a waterpermeable membrane having a pattern of curable composition spacersprinted thereon, where the curable composition spacers are formed from alight curable composition which viscosity of the curable composition is10,000 to 500,000 centipoise (cP) at 10 s⁻¹, a Thixotropic Index (TI)(viscosity at 1 s⁻¹/viscosity at 10 s⁻¹), of between about 2 and about15, where the spacers have been formed by stencil printing or screenprinting one or more spacer layers having an aspect ratio (height/width)between about 0.2 and about 2.

There is provided a method of manufacturing a filtration membrane havingprinted curable composition spacers including the steps of providing amembrane have a first surface and an opposing second surface; anddepositing a light curable composition onto the first and/or secondmembrane surface(s) to form spacer features having a defined shape andsize; wherein the light curable composition has viscosity of 10,000 to500,000 centipoise (cP) at 10 s⁻¹, a Thixotropic Index (TI) (viscosityat 1 s⁻¹/ viscosity at 10 s⁻¹) of between about 2 and about 15 and wherethe aspect ratio (height/width) of the curable composition is betweenabout 0.2 and about 2.

EXAMPLES Example 1−UV/Visible Light Curable Compositions

Table 1 shows the ingredients of nine UV/visible light curable acrylatecompositions. Compositions 1-3 have different amounts of fumed silica asthe rheology modifying component. Compositions 4-5 have silica andsilicate as rheology modifying components. Composition 6 hasprecipitated silica as the rheology modifying component. Composition 7,8 and 9 have calcium carbonate, alumina and micronized polypropylenepowder as rheology modifying components, respectively, in addition tosilica.

TABLE 1 Curable Composition 1 2 3 4 5 6 7 8 9 Ingredient Wt % Wt % Wt %Wt % Wt % Wt % Wt % Wt % Wt % Polyester Urethane 57.60 55.20 52.80 37.2037.20 51.00 38.40 38.40 33.00 acrylate Isobornyl acrylate 26.88 25.7624.64 17.36 17.36 23.80 17.92 17.92 18.48 Isodecyl acrylate 9.60 9.208.80 6.20 6.20 8.50 6.40 6.40 13.20 Irgacure 184 0.96 0.92 0.88 0.620.62 0.85 0.64 0.64 0.66 Irgacure TPO 0.96 0.92 0.88 0.62 0.62 0.85 0.640.64 0.66 Aerosil R202 4.00 8.00 12.00 8.00 8.00 6.00 6.00 4.00 Aluminumsilicate 325 30.00 mesh Zirconium silicate 400 30.00 mesh Zeothix 95Precipated 15.00 silica Solca 322 acid modified 30.00 Calcium carbonateCalcined alumina 30.00 Polypropylene powder 30.00 Total 100 100 100 100100 100 100 100 100

Example 2−Rheology of UV/Visible Light Curable Compositions

Table 2 summarizes the rheological properties (viscosity and ThixotropicIndex (TI)) of the nine compositions of Example 1. Viscosities weremeasured at shear rate of 1 s⁻¹ and 10 s⁻¹ using cone and platerheometer (Anton Paar). Thixotropic Index (TI) was calculated as theratio of viscosities at 1 s⁻¹ and 10 s⁻¹.

TABLE 2 Viscosity at 1 Viscosity at 10 Thixotropic s⁻¹ s⁻¹ IndexComposition (cP) (cP) (TI) 1 37,580 6,138 6.12 2 387,700 48,680 7.96 31,306,000 138,000 9.46 4 725,900 93,700 7.75 5 955,500 113,800 8.40 6211,400 16,920 12.49 7 2,377,000 75,790 31.36 8 458,000 51,640 8.87 9100,500 12,570 8.00

Example 3−Chemical Resistance of UV/Visible Light Cure Compositions

Table 3 summarizes the results (as percent weight change) of chemicalresistance testing of some of the UV/visible light curable compositionsshown in Table 1. The light curable composition was placed between twoplastic sheets with lmm thick spacer, and light cured for 30 seconds ina UV chamber with UV A light intensity of 100 mw/cm². The cured sheetwas cut into 20 mm long and 10 mm wide rectangular specimen. Thespecimen was then immersed in pH 1.5 hydrochloric acid solution or pH12.5 sodium hydroxide solution for 2 weeks at 50° C.

After immersion, the specimen was rinsed with distilled water and driedat 50° C. for 4 hours. The weight change (%) was calculated by theweight percent difference of the specimen before and after immersion.For comparison, a commercial light cure adhesive (Loctite LT AA3979) wasalso tested.

TABLE 3 pH 1.5 pH 12.5 Composition Solution Solution 1 −0.87 −2.07 4−0.35 −4.05 5 −0.31 −2.38 6 −1.00 −29.90 7 −4.11 −7.70 8 −0.56 −3.19 9−0.67 −2.16 Loctite LT AA 3979 −12.31 −28.36

Among the fillers used, Aerosil R202 and zirconium silicate had lessthan 3% weight loss after 2 weeks immersion in both pH 1.5 and 12.5solutions. Weight change of formulations with Calcined Alumina oraluminium silicate was less than 4%. However, the formulas withprecipitated silica had very poor chemical resistance in pH 12.5solution. The formulas with calcium carbonate had poor chemicalresistance in both pH 1.5 and 12.5 solutions. Loctite AA 3979 had theworst chemical resistance in both pH 1.5 and 12.5 solutions due to theacrylate resins used in the formulas.

Comparative Example 1−Comparison of Various Existing Adhesives andDispensing Methods

Optimized rheology is required for the printability of the curablecomposition while also having the desired aspect ratio to optimize themembrane's surface area. Moreover, the cure speed is also a criticalfactor in the manufacturing method. Table 4 is a comparison of someexisting dispensing methods using different products. This table listsseveral categories of products, their viscosity, the dispensing methodused, and the targeted feature height, feature width and aspect ratio.The curing time for single dispensed material using the correspondingdispensing method, and the produced area (m²)per minute with thetargeted features are also shown in Table 4. The target width was 0.020inch with a target processing speed of at least 2 m² per minute.

UV ink with low viscosity is generally used for ink jet printing. Itprints a very thin layer each time, therefore it takes long time toproduce the feature heights. Jet valve dispensing using liquid or gellight cure acrylate (LCA) with higher viscosity has similar issues oflow speed. Hot melt material such as polyolefine (PO) has high producingspeed, but has difficulty achieving a high aspect ratio.

As shown in Table 4, UV Ink and Gel LCA achieve a good aspect ratio, POHot Melt achieves an adequate aspect ratio, and Liquid LCA achieves anunacceptable aspect ratio. UV Ink, Gel LCA, and Liquid LCA have a goodcure time and PO Hot Melt has an unacceptable cure time. UV Ink, GelLCA, and Liquid LCA have an unacceptable production (area m²) per minuteand PO Hot Melt has a good production (area m²) per minute. Accordingly,none of these existing methods achieved acceptable overall results.

TABLE 4 Category of Product UV Ink UV Ink Liquid LCA Gel LCA Gel LCA POHot Melt Typical Viscosity (cP) 10 10 5,000 50,000 50,000 12,000 (at170° C.) Dispense Method Ink Jet Ink Jet Jet Valve Jet Valve TouchTransfer Gravure Feature Height (in) 0.015 0.018 0.010 0.015 0.015 0.012Feature Width (in) 0.025 0.044 0.065 0.033 0.022 0.022 Feature AspectRatio (H/W) 0.60 0.40 0.15 0.45 0.66 0.31 Cure Time (sec) 1 1 5 5 5 30Production (Area (m²)) 0.016 0.014 0.026 0.026 Too Slow, 100 per minuten/a

Example 4−Stencil Printability of UV/Visible Light Cure Compositions

Table 5 shows the results of the stencil printability measurement of theUV/visible light cure compositions in Table 1. For stencil printing,each material was applied to a Nanoclear (Aculon) coated steel stencilwith aperture size of 0.15 inch×0.02 inch and thickness of 0.01 inch.The material was manually printed onto a membrane using a polyurethaneDurometer 70 squeegee. The printed pattern on the membrane wasimmediately transferred to a UV chamber with UV A light intensity of 100mw/cm² and cured for 10 seconds, or cured for 3 seconds using a 405 nmLED light with intensity of 90 mw/cm². The initial printability wasevaluated for the cleanness of the curable composition separated fromstencil aperture after printing and lifting the stencil, the printedpattern surface smoothness and if the shape slumped.

TABLE 5 Curable Composition Printed Release from Pattern Printed CurableStencil Surface Pattern Composition Aperture Appearance Shape 1 PartialSmooth Slumped 2 Partial Smooth Good 3 Partial Not Smooth Good 4 GoodSmooth Good 5 Good Smooth Good 6 Good Smooth Good 7 Good Smooth Good 8Good Smooth Good 9 Good Smooth Good

Example 5−Stencil Printed Pattern of UV/Visible Light Cure Compositionswith Wet Printing

Curable Compositions 5 and 9 in Table 1 having relatively betterchemical resistance and stencil printability were used for furtherstudies. Wet printing means that the conventional stencil printing wasemployed, i.e., the curable composition was printed on the substrate,the stencil was lifted, and then the curable composition was cured.

The curable composition was printed on a membrane using semi-automatedprinter with a coated stainless steel (SS) stencil or plastic stencil.The stencil aperture had 0.02 inch width, 0.015 inch length. Thicknessof coated stainless stencil was 0.012 inch, 0.017 inch and 0.022 inch,respectively. The thickness of plastic stencil was 0.01 inch. Theprinted dimensions of Composition 5 using coated stainless stencil andComposition 6 using plastic stencil were shown in Table 6 (wetprinting). The length and width of the printed pattern were measured byHirox microscopy. The thickness was measured by a Laser profilometer.Aspect ratio was calculated as the ratio of height to width.

TABLE 6 Printed Pattern Height Width Length Aspect Cure Produced AreaDimensions (inch) (inch) (inch) Ratio Speed (s) (m²) per min 0.012 inchthick 0.007 0.023 0.148 0.30 5 3 Coated SS Stencil 0.01 inch thick 0.0090.024 0.152 0.38 5 3 Plastic Stencil 0.017 inch thick 0.014 0.026 0.1500.54 5 3 Coated SS Stencil 0.022 inch thick Composition was partiallyreleased Coated SS Stencil

The curing speed and production speed by stencil printing was fasterthan most of the existing dispensing methods in Table 4. The printedresults showed printed pattern using wet printing can achieve aspectratio around 0.5. However, it is technically challenging to producepatterns with higher aspect ratios than 0.5.

Example 6−Stencil Printed Pattern of UV/Visible Light Cure Compositionswith Pre-Cure Method

In this example, the materials, stencils, printer and printed patternmeasurement methods were the same as Example 5. A pre-cure method wasused to increase the printed pattern aspect ratio. In the pre-curemethod the curable composition was printed on the substrate, and beforethe stencil was lifted, the curable composition in the stencil aperturewas partially light cured from the back of the membrane and its holder.The curable composition became solid on the part touching the membranebut remained uncured on the stencil surface. The stencil was then liftedand separated from membrane. The printed pattern stayed on the membraneand was further light cured to reach its full cured properties.

The printed dimensions of Composition 5 using Coated SS Stencil andComposition 6 using Plastic Stencil with 0.03 inch thickness are shownin Table 7 (pre-cure method).

TABLE 7 Printed Pattern Height Width Length Aspect Cure Produced AreaDimensions (inch) (inch) (inch) Ratio Speed (s) (m²) per min 0.022 inchthick 0.017 0.025 0.152 0.68 7 2 Coated SS Stencil 0.03 inch thick 0.0290.021 0.151 1.38 7 2 Coated SS Stencil

The results in Table 7 show that the aspect ratio can be improved byusing the pre-cure method with little reduction of production speed.

1. A method of forming topographical features on a membrane surfacecomprising: providing a membrane surface; providing a stencil or screenover the membrane surface, the stencil or screen having openingsexposing the membrane surface for receiving a curable composition;depositing one or more layers of curable composition into the stencilopenings or screen openings and onto the membrane surface to form thetopographical features, the openings defining an approximate shape andsize of the topographical features; removing the stencil or screen toleave in place the topographical features on the membrane; and curingthe curable composition, wherein a single layer of the curablecomposition deposited in the depositing step produces topographicalfeatures have an aspect ratio (height/width) from about 0.2 to about 2.2. The method of claim 1, wherein the removing the stencil or screenstep occurs before the curing step.
 3. The method of claim 1, whereinthe curing step occurs before the removing the stencil or screen step.4. The method of claim 1, wherein the curing step comprises: a) apre-cure step occurring before the removing the stencil or screen stepduring which the curable composition is partially cured and b) a fullcure step occurring after the removing the stencil or screen step duringwhich the curable composition is fully cured.
 5. The method of claim 4,wherein pre-cure step comprises exposing the side of the membranewithout the topographical features to a light source.
 6. The method ofclaim 1, wherein the aspect ratio (height/width) is greater than about0.50.
 7. The method of claim 1, wherein the topographical aspect ratio(height/width) is greater than about 0.70.
 8. The method of claim 1,wherein the height of the topographical feature is from about 0.005 toabout 0.04 inches.
 9. The method of claim 1, wherein the curablecomposition is cured using a light source.
 10. The method of claim 9,wherein the light source produces ultraviolet or visible light.
 11. Themethod of claim 9, wherein the light source is a bulb or light emittingdiode.
 12. The method of claim 1, wherein a pattern of topographicalfeatures is formed on the membrane surface at speeds of about 0.5m²/minute or greater.
 13. The method of claim 1, wherein the depositingstep comprises depositing two or more layers of curable composition intothe stencil openings or screen openings and onto the membrane surface.14. The method of claim 1, wherein the topographical features aresubstantially free of sharp edges after formation and removal of thestencil.
 15. The method of claim 1, wherein the membrane surface is afilter membrane surface.
 16. A method of forming topographical featureson a membrane surface comprising: providing a membrane surface;providing a stencil or screen over the membrane surface, the stencil orscreen having openings exposing the membrane surface for receiving acurable composition ; depositing one or more layers of curablecomposition into the stencil openings or screen openings and onto themembrane surface to form the topographical features, the openingsdefining an approximate shape and size of the topographical features;and removing the stencil or screen to leave in place the topographicalfeatures on the membrane; wherein the Thixotropic index (TI) (cp at 1s⁻¹/cp at 10 s⁻¹) of the curable composition is about 2 to about 15, andthe curable composition provides a topographical features aspect ratio(height/width) sufficient to substantially maintain the approximate sizeand shape of the feature during removal of the stencil from the membranesurface prior to cure.
 17. The method of claim 16, wherein thetopographical aspect ratio (height/width) is between about 0.2 to about2.
 18. The method of claim 16, wherein the topographical aspect ratio(height/width) is greater than about 0.50.
 19. The method of claim 16,wherein the topographical aspect ratio (height/width) is between greaterthan about 0.70.
 20. The method of claim 16, wherein the height of thetopographical feature is from about 0.005 to about 0.04 inches.
 21. Themethod of claim 16, wherein the curable composition is cured using alight source.
 22. The method of claim 21 wherein the light sourceproduces ultraviolet or visible light.
 23. The method of claim 21,wherein the light source is a bulb or light emitting diode.
 24. Themethod of claim 16, wherein a pattern of topographical features isformed on the membrane surface at speeds of about 0.5 m²/minute orgreater.
 25. The method of claim 16, wherein the depositing stepcomprises depositing two or more layers of curable composition into thestencil openings or screen openings and onto the membrane surface. 26.The method of claim 16, wherein the topographical features aresubstantially free of sharp edges after formation and removal of thestencil.
 27. The method of claim 16, wherein the membrane surface is afilter membrane surface.
 28. A light curable composition comprising: a.a light curable component comprising a backbone selected from the groupconsisting of (meth)acrylates, epoxies, polyisobutenes (PIB),polyurethanes (PU), polyolefins (PO), ethylvinylacetates (EVA),polyamides (PA) and combinations thereof; and a light curing moiety; b.a cure system; and c. a rheology modifying component present in anamount of about 2% to about 50% by weight of the total curablecomposition; wherein the light curable composition has a ThixotropicIndex (TI) (cp at 1 s⁻¹/cp at 10 s⁻¹) of between about 2 and about 15.29. The light curable composition of claim 28, wherein the curecomponent comprises an ultraviolet light cure component or visible lightcure component.
 30. The light curable composition of claim 28, whereinthe rheology modifying component is selected from the group consistingof silica, silicate, alumina, asbestos, barium sulphate, calciumcarbonate, calcium fluoride, carbon black, clays, diatomaceous earth,feldspar, ferromagnetics, fly ash, glass fibers, gypsum, jute fiber,kaolin, lingnocellulosics, magnesium hydroxide, mica, microcrystallinecellulose, powdered metals, quartz, startch, talc, titanium dioxide,wood flour, wood fibers, thermoplastic poymers, and combinationsthereof.
 31. The light curable composition of claim 28, wherein thelight curable composition subsequent to cure is capable of less thanabout 5% weight loss when submerged in a aqueous solution at a pH rangeof about 0.5 to about 13.5 at temperatures of from about 25° C. to about90° C. for in a 6 week period.
 32. The light curable composition ofclaim 28, wherein the light curable composition is capable of formingand maintaining topographical surface features having an aspect ratio(height/width) of between about 0.2 to about 2 prior to full cure. 33.The light curable composition of claim 28, wherein the light curablecomponent comprises a material selected from the group consisting of aurethane (meth)acrylate and a (meth)acylate.
 34. A reverse osmosisfilter comprising: a. a water permeable membrane having a pattern ofcurable composition spacers printed thereon, wherein the curablecomposition spacers are formed from a light curable composition which aThixotropic Index (TI) (cp at 1 s⁻¹/cp at 10 s⁻¹) of between about 2 andabout 15, wherein the spacers are formed by stencil printing or screenprinting one or more spacer layers having an aspect ratio(height/width)between about 0.2 and about
 2. 35. A method ofmanufacturing a filtration membrane having printed curable compositionspacers comprising: providing a membrane have a first surface and anopposing second surface; and depositing a light curable composition ontothe first and/or second membrane surface(s) to form spacer featureshaving a defined shape and size; wherein the light curable compositionhas is a a Thixotropic Index (TI) (cp at 1 s⁻¹/cp at 10 s⁻¹) of betweenabout 2 and about 15 and wherein the aspect ratio (height/width) of thelight curable composition is between about 0.2 and about 2.